The core period of YOPP, which took place from mid-2017 to mid-2019, entailed periods of enhanced observational and modelling campaigns in both the Arctic and the Antarctic. As a direct outcome of the YOPP planning meetings on "YOPP in the Southern Hemisphere" (June 2016, Columbus, Ohio, USA), and on "Arctic Observations and the YOPP Modelling Component" (September 2016, Reading, UK), it was decided to carry out Special Observing Periods (SOPs) during the YOPP Core Phase. The purpose of the SOPs was to enhance the routine observations, particularly but not exclusively radiosondes, in an attempt to close the gaps in the conventional Arctic and Antarctic observing systems for an extended period of time (several weeks). This has allowed to carry out subsequent forecasting system experiments aimed at optimizing observing systems in the polar regions and providing insight into the impact of better polar observations on forecast skills in lower latitudes to be carried out.
The following three Special Observing Periods took place (click to enlarge
figure on the right):
- February 1st to March 31st, 2018 in the Arctic,
- July 1st to September 30th, 2018 in the Arctic, and
- November 16th, 2018 to February 15th, 2019 in the Antarctic.
- April 14, 2022 to August 31, 2022 in the Antarctic.
The main objective of the YOPP Special Observing Periods (SOPs) during 2018/19 and the 2022 Antarctic SOP was to assess the impact of increased frequency of observations in the polar regions. Preliminary results from observing system experiments (OSEs) suggest that on average this led to only minor improvement in prediction skill but there were larger impacts during certain large-scale flow situations. Therefore, the PPP Steering Group decided at its tenth meeting in Helsinki in January 2019 to revise the concept for additional observations and to target episodes of particularly strong Arctic-mid-latitude linkages and their associated air mass modifications. This approach capitalized on the increasingly strong partnership that was built between YOPP and MOSAiC observing assets.
Targeted Observing Periods (TOPs)
Targeted Observing Periods (TOPs) refers to the practise of undertaking additional observations to capture enhanced details for specific weather events in particular areas. TOPs in the Arctic took place in spring/summer 2020, aligned with the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) – the first year-round expedition in the central Arctic that provided a quantum leap in our understanding of critical Arctic processes and their representation in weather and climate models.The focus of the YOPP Targeted Observing Periods planned during the MOSAiC experiment was on increasing atmospheric observations including radiosonde flights during episodes of strong interactions between the Arctic and mid-latitudes, i.e. warm air intrusions and cold air outbreaks. The TOP approach was also used during the Antarctic Winter SOP in 2022 to investigate atmospheric river events in the Antarctic Peninsula area and the interaction of major cyclonic systems with Antarctica in the Eastern Antarctic.
See further information on TOPs on the Model Intercomparision adn Improvement Project (MIIP) webpage.
What was done during the SOPs and TOPs?
Firstly, it was critical that as many observations as possible were shared through the WMO Global Telecommunication System (GTS) to make them accessible to operational prediction centres in real time. Secondly, it was important to enhance the current observation network by: a) more frequent observations from existing platforms and/or b) adding observations in regions where the routine synoptic observation network is not sufficiently dense. The additional observational data was complemented by additional NWP data being archived for specific sites in the Arctic and Antarctica to allow comparison between the two data types in an effort to improve model parameterisation and identify the causes of systematic model error. To this end model tendency data at individual timesteps as well as the normal model output was gathered and stored. The MIIP activity continues to review and analyse these rich data sets.